JP2019206986A - Rolling bearing, and manufacturing method of rolling bearing - Google Patents

Abstract

To provide a rolling bearing and a manufacturing method of the rolling bearing capable of suppressing surface layer starting point type separation in a bearing not sharing a lubricant with other components, for example, HUB and a bearing for an electric motor.SOLUTION: Compressive residual stress is applied to surface layers of raceway surfaces of an inner ring and an outer ring, in a rolling bearing in which rolling elements are rollably retained between the inner ring and the outer ring, and a lubricant is not shared with other components.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a rolling bearing and a method for manufacturing a rolling bearing.

  The life of a rolling bearing is determined by a standard such as ISO, and it is required to ensure the life until a specified period. The life of a bearing is often influenced by peeling. For example, when foreign matter or the like is mixed during use, peeling occurs from an indentation generated by the biting of the foreign matter. In addition, by the same mechanism, minute continuous peeling called peeling occurs in a depleted lubrication environment. Such peeling has a shorter life compared to peeling that occurs in a good lubricating environment. For this reason, for example, the lifetime has been extended by increasing the retained austenite on the surface by using a heat treatment such as carbonitriding. In addition, in the case where contamination is caused by foreign matters, it is extremely effective to devise a seal structure so that foreign matters do not easily enter the bearing. For this reason, measures are also taken by eliminating the cause of contamination. Such countermeasures are determined especially when the lubricant is shared with other parts such as gears, such as automobile transmission bearings. It is effective when it is not possible.

  On the other hand, bearings are basically recommended to be used in a good lubrication environment suitable for bearings, and this is normal for general applications. Examples of such bearings include HUB and electric motor bearings. Under a good lubricating environment, the service life is good, which is obtained as a result of reducing the nonmetallic inclusions (hereinafter also simply referred to as “inclusions”) generated in the steelmaking stage to the limit. However, it is almost impossible to completely remove such inclusions in mass production, and as mentioned above, the countermeasures for short life due to external factors have been taken. There is a need for further measures against peeling.

As described above, inclusions are inevitable impurities generated during steelmaking, and it is almost impossible to eliminate them completely in the current mass production process. In view of this, a technique has been proposed in which the number of inclusions in the material is reduced as much as possible to suppress separation. For example, Patent Document 1 discloses that the number of sulfide inclusions having a thickness of 1 μm or more existing in a test area of 320 mm ² and the maximum diameter of oxide inclusions are controlled to 10 μm or less, thereby extending the life. A bearing steel is disclosed. Patent Document 2 discloses a bearing steel having a long life by defining 100 to 200 oxide inclusions existing in a test area of 320 mm ² and further defining the amount of Sb as an impurity element. It is disclosed.

Japanese Patent No. 3338761 Japanese Patent No. 3779078

However, as in Patent Documents 1 and 2, even if the number and size of inclusions in a small test area are specified, in an actual bearing, the largest inclusion existing in a portion where high stress is applied Since peeling occurs as a starting point, the peeling life may be unexpectedly shortened. In particular, an effective effect cannot be expected for a surface-origin type delamination that is a delamination caused by the occurrence and propagation of a crack starting from the largest inclusion existing in the surface of the raceway surface of the bearing.
Therefore, the present invention has been made paying attention to the above-mentioned problems, and for example, suppresses surface layer-type separation in bearings that do not share lubricating oil with other components such as HUBs and motor bearings. It is an object of the present invention to provide a rolling bearing and a method for manufacturing the rolling bearing. It should be noted that the surface-origin type peeling described here is not only the peeling from the inclusions partially exposed on the surface, but also the peeling from the inclusions existing at the position that can be regarded as equivalent to this. Indicates. That is, the surface layer origin-type separation is a separation starting from an inclusion existing at a position shallower than the maximum shear stress depth.

According to one aspect of the present invention, a rolling bearing is provided that freely rolls between an inner ring and an outer ring and does not share lubricating oil with other parts, and the races of the inner ring and the outer ring. There is provided a rolling bearing characterized in that a compressive residual stress is applied to a surface layer of the surface.
According to one aspect of the present invention, there is provided a method of manufacturing a rolling bearing in which a rolling element is rotatably held between an inner ring and an outer ring and does not share lubricating oil with other components, the inner ring and the A rolling bearing manufacturing method is provided, in which after the outer ring is quenched and tempered, compressive residual stress is applied to the raceways of the inner ring and the outer ring.

  According to one aspect of the present invention, for example, in a bearing that does not share lubricating oil with other components such as a HUB and a motor bearing, the rolling bearing and the rolling bearing can be manufactured that can suppress the separation of the surface-origin type. A method is provided.

It is a partially cutaway perspective view showing a radial ball bearing which is an example of a rolling bearing according to an embodiment of the present invention. It is a graph explaining the preferable example of distribution of the compressive residual stress of the raceway surface layer of a rolling bearing. It is a schematic diagram which shows the process by roller burnishing. It is a graph which shows the measurement result of the compressive residual stress by X-ray diffraction in an Example. It is a graph which shows the result of a rolling fatigue life test in an Example.

  In the following detailed description, numerous specific details are set forth, illustrating embodiments of the present invention, in order to provide a thorough understanding of the present invention. It will be apparent, however, that one or more embodiments may be practiced without such specific details. In the drawings, for the sake of brevity, well-known structures and devices are schematically shown.

<Rolling bearing>
A rolling bearing according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. The rolling bearing according to the present embodiment is a rolling bearing in which a rolling element is movably held between an inner ring and an outer ring, and there is no limitation on the type or configuration. For example, as a rolling bearing, a radial ball bearing or a radial tapered roller bearing can be targeted. FIG. 1 shows a radial ball bearing 1 as an example of a rolling bearing. The radial ball bearing 1 includes an outer ring 2 having an outer ring raceway 21 on an inner peripheral surface, an inner ring 3 having an inner ring raceway 31 on an outer peripheral surface, and an annular crown type between the outer ring raceway 21 and the inner ring raceway 31. A plurality of balls 5 each provided as a rolling element are provided so as to be able to roll while being held by the cage 4.

  In addition, the rolling bearing according to the present embodiment is a bearing that does not share lubricating oil with other parts other than the bearing. Examples of bearings that do not share lubricating oil with other components include HUB and motor bearings, sealed rolling bearings with seals or shield plates, and rolling bearings that do not have a sealing device used in a good lubricating environment. . Such a bearing is used in a good lubrication environment and does not share lubricating oil with other components, so that almost no foreign matter is mixed therein.

  Furthermore, in an unused (new) state, compressive residual stress is applied to the raceway surface layer of the rolling bearing. The depth to which the compressive residual stress is applied from the raceway surface of the rolling bearing is the maximum of inclusions targeted for surface layer-type separation control (hereinafter also simply referred to as “target inclusions”). It is set according to the diameter, and is preferably at least 50% or more of the maximum diameter of the target inclusion. For example, when the maximum diameter of the target inclusion is 100 μm, compressive residual stress is applied to a region having a depth of 50 μm from the surface of the raceway surface. In addition, from the viewpoint of suppressing delamination of the surface layer starting type, there is no problem even if the depth for applying compressive residual stress is deeper than the above range, but the cost for processing for applying compressive residual stress is high. Increase. For this reason, it is preferable to determine the depth to which the compressive residual stress is applied, from the viewpoints of both the effect of suppressing surface layer-type separation and the cost of processing.

  In addition, it is preferable that the maximum diameter of the inclusions to be targeted is a value in the range of 100 μm or less. Inclusions with a maximum diameter of 100 μm or less may be inevitably mixed at a certain probability in general bearing inspections. Bearing steel in which these inclusions are completely removed from the surface layer of the raceway surface. This is very difficult in terms of inspection accuracy and cost. On the other hand, inclusions having a diameter of more than 100 μm can be detected with high accuracy in a general bearing inspection.

  Further, in the unused state, the surface of the raceway surface of the rolling bearing has a maximum compressive residual stress (maximum in absolute value) at a predetermined depth from the surface according to the maximum diameter of the target inclusion. It is preferable that the compressive residual stress is applied in a distribution having a peak. The predetermined depth is preferably 40% or more and 60% or less of the maximum diameter of the inclusion, and more preferably about 50%. FIG. 2 shows an example of a preferable distribution of the compressive residual stress on the raceway surface layer of the rolling bearing. In FIG. 2, the horizontal axis indicates the position in the depth direction from the raceway surface in the raceway surface layer of the rolling bearing, and the vertical axis indicates the compressive residual stress. Compressive residual stress is applied so as to have a maximum peak at a depth of 50 μm, which is 50% of the maximum diameter of the target inclusion. By creating a compressive residual stress distribution that has a compressive residual stress peak at a depth of 50% of the maximum diameter of the inclusions, it is possible to suppress the generation and propagation of cracks from around the inclusions. Become. For this reason, it becomes possible to suppress generation | occurrence | production of peeling by the surface layer, ie, the inclusion which exists in a position shallower than the maximum shear stress depth. That is, it is preferable to have a peak of compressive residual stress as illustrated in FIG.

<Rolling bearing manufacturing method>
Next, the manufacturing method of the rolling bearing which concerns on this embodiment is demonstrated. In the present embodiment, first, a steel material, which is a material, is processed into a predetermined shape according to the product shape, and subjected to quenching and tempering treatment to obtain an inner ring, an outer ring, and a rolling element. As the steel material, for example, general-purpose bearing steel such as SUJ2 or SUJ3 can be used. In addition, the magnitude of the residual stress introduced by the process of the present embodiment described later is larger than the value introduced by a general heat treatment, and is useful even when using a surface hardening type heat treatment such as carburizing or carbonitriding. It can be applied to any steel material or heat treatment generally used for bearings. In particular, carburized steel has a low carbon content of the base material, and therefore there is a tendency for the inclusions in the steel material to be larger than in bearing steel, and the effect of this method can be expected.

  Next, compressive residual stress is applied to the raceway surface layer of the inner ring and the outer ring (also collectively referred to as “track ring”). For applying compressive residual stress, any method can be used as long as compressive residual stress of the above conditions such as the depth and distribution to be applied can be applied to the raceway surface layer of the finally produced raceway ring. Also good. As a method for applying the compressive residual stress, for example, shot peening or roller burnishing can be used. When shot peening is used, processing conditions such as the size, material, and speed of the projection material to be collided are appropriately set so as to satisfy the target compressive residual stress condition. Further, when roller burnishing is used, a roller matching the shape of the raceway surface of the raceway is brought into compression-rotation contact with the raceway surface of the raceway ring to give a minute plastic deformation to the raceway surface. In this case, the roller burnishing processing conditions such as the material of the roller to be used and the rolling pressure are appropriately set so as to satisfy the target compressive residual stress condition. In FIG. 3, as an example of roller burnishing, a model for applying residual stress to the outer ring raceway 21 of the outer ring 2 of the radial ball bearing 1 using a roller burnishing device 6 provided with a spherical ball 61 having a high hardness at the tip. The figure is shown. In the example shown in FIG. 3, while rotating the outer ring 2 around its own axis, the ball 61 is pressed against the outer ring raceway 21 which is the inner peripheral surface of the outer ring 2, and the ball 61 is brought into compression contact with the outer ring raceway 21. In this state, the roller burnishing device 6 is moved along the generatrix direction of the inner peripheral surface according to the shape of the inner peripheral surface of the outer ring 2, whereby the compressive residual stress is applied by the roller burnishing device 6.

After the application of the compressive residual stress, the finishing of the raceway is performed as necessary. In the finishing process, a cutting process or a polishing process is performed to smooth the raceway surface to which the compressive residual stress is applied. In particular, when compressive residual stress is applied using shot peening, since the raceway surface is uneven, for example, a finishing process of cutting the raceway surface by about 30 μm to 40 μm is performed. Further, when compressive residual stress is applied using roller burnishing and the raceway surface is sufficiently smooth, finishing may not be performed. Further, if necessary, heat treatment such as tempering may be performed on the raceway before finishing.
And the rolling bearing used as a product is manufactured by combining the bearing ring and rolling element manufactured by the above-mentioned method, and the general purpose holder produced separately.

<Modification>
Although the present invention has been described above with reference to specific embodiments, it is not intended that the present invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention will be apparent to those skilled in the art, including various modifications along with the disclosed embodiments. Therefore, it should be understood that the embodiments of the present invention described in the claims also include embodiments including these modifications described in the present specification alone or in combination.

  For example, in the above embodiment, shot peening or roller burnishing is used as an example of a method for applying compressive residual stress, but the present invention is not limited to such an example. Other methods may be used to apply the compressive residual stress as long as the method can apply the compressive residual stress of the target condition. Since it is preferable to apply the compressive residual stress only to the raceway surface layer, a method of mechanically applying the compressive residual stress to the raceway surface layer, such as shot peening or roller burnishing, is preferable.

<Effect of embodiment>
(1) A rolling bearing according to an aspect of the present invention is a rolling bearing in which a rolling element is movably held between an inner ring and an outer ring, and does not share lubricating oil with other components. A compressive residual stress is applied to the surface layer of the raceway surface of the outer ring.
According to the configuration of (1) above, by applying compressive residual stress to the raceway surface layer, it is possible to suppress the progress of cracks starting from the inclusions on the raceway surface layer, and to prevent the occurrence of delamination of the surface layer type. Can be suppressed. Thereby, the lifetime of a rolling bearing can be extended. In particular, in a low-grade rolling bearing that is inevitably included with the probability that there is an inclusion having a large maximum diameter, the surface-origin type separation that occurs suddenly becomes a problem. However, by applying compressive residual stress to the surface of the raceway surface, it becomes possible to use such a low-grade rolling bearing with a stable life.

(2) In the configuration of (1), the distribution of compressive residual stress in the depth direction from the surface of the raceway surface is such that the compressive residual stress is maximum at a depth of 40 μm or more and 60 μm or less from the surface of the raceway surface. The peak is located.
According to the configuration of (2) above, it is possible to suppress the occurrence of delamination of the surface layer starting type starting from inclusions having a maximum diameter of about 100 μm or less.

(3) A rolling bearing manufacturing method according to an aspect of the present invention is a rolling bearing manufacturing method in which a rolling element is rotatably held between an inner ring and an outer ring, and the lubricating oil is not shared with other components. In this case, after quenching and tempering the inner ring and the outer ring, compressive residual stress is applied to the raceways of the inner ring and the outer ring.
According to the configuration of (3) above, the same effect as the configuration of (1) can be obtained.

(4) In the configuration of (3) above, when compressive residual stress is applied to the raceway surface, the compressive residual stress is from the surface of the raceway surface to a depth of 40% to 60% of the maximum diameter of inclusions. Applying compressive residual stress so that the maximum peak is located According to the configuration of (4) above, applying compressive residual stress to an appropriate depth according to the maximum diameter of the inclusions of interest Can do. The deeper the depth to which compressive residual stress is applied, the more the occurrence of delamination of the surface layer starting type starting from inclusions having a larger diameter can be suppressed. However, as the depth for applying the compressive residual stress increases, the time and cost for processing tend to increase. For this reason, depending on the difference in materials and the grade (quality) of bearing steel, the maximum diameter of the inclusions targeted is changed, and by applying compressive residual stress to the appropriate depth accordingly, the surface origin It is possible to achieve both suppression of mold peeling and reduction of cost for manufacturing a rolling bearing.

(5) In the configuration of (4) above, the maximum diameter of inclusions is set to a value in the range of 100 μm or less.
According to the configuration of the above (5), in a general bearing inspection, it is possible to suppress the occurrence of delamination of the surface layer starting type starting from inclusions of a size that may be inevitably mixed with a certain probability. be able to.

Next, examples performed by the present inventors will be described. In the examples, the effect of suppressing the progress of cracks starting from inclusions present on the bearing surface of the bearing due to compressive residual stress was examined.
In the example, the rolling bearing was manufactured under the two conditions of Example 1 and Example 2 with different manufacturing conditions by using shot peening as a method of applying compressive residual stress.

In Example 1, bearing rings and rolling elements were made from SUJ2 which is a bearing steel, and quenched and tempered. After that, the bearings were shot peened and finished to produce rolling bearings.
In Example 2, similarly to Example 1, bearing rings and rolling elements were made from SUJ2 which is bearing steel, and quenched and tempered. Thereafter, the bearing ring was shot peened, tempered (240 ° C. × 2 h), and then finished to produce a rolling bearing.

Further, in the examples, as a comparison, a rolling bearing was manufactured even under a condition in which compressive residual stress was not applied to the race (comparative example). In the comparative example, similarly to Example 1, bearing rings and rolling elements were made from SUJ2 which is bearing steel, and quenching and tempering were performed. Then, the rolling bearing was manufactured by performing finish processing similarly to Example 1 without performing shot peening.
FIG. 4 and Table 1 show the measurement results by X-ray diffraction of the compressive residual stress from the raceway surface to a depth of 200 μm in the raceway surfaces of the rolling bearings of Examples 1 and 2 and the comparative example. As shown in FIG. 4 and Table 1, it was confirmed that under the conditions of Examples 1 and 2, compressive residual stress was applied to a depth of 100 μm or more even after finishing. Moreover, it was confirmed that the distribution of compressive residual stress differs between Example 1 and Example 2 depending on the presence or absence of tempering after shot peening. Further, according to the results shown in Table 1, with respect to the distribution of the compressive residual stress in the depth direction from the surface of the raceway surface, the compressive residual stress is maximized at a depth of 40 μm or more and 60 μm or less from the surface of the raceway surface. It was found that the peak was located. That is, in Examples 1 and 2, the compressive residual stress is maximum at a depth of 50 μm.

Furthermore, in the examples, for the rolling bearings manufactured under the conditions of Examples 1 and 2 and the comparative example, artificial defects were imparted to the raceway surface, and a rolling fatigue life test was performed. In the life test, in order to quantify the peel strength of rolling bearings, a report was given in which micro drill holes were provided on the bearing raceway surface and cracks were generated and evaluated from the edge of the drill hole (Hashimoto et al., “ Effect of micro-defect size (2nd report: Evaluation of peel strength of rolling bearings with drill holes based on stress intensity factor) ", Transactions of the Japan Society of Mechanical Engineers, Vol.83, No.852 (2017), P1-P12) The test was conducted using the same method as described above. Specifically, as an artificial defect, a drill hole having a size of φ100 × 50 μm was provided on the raceway surface in order to simulate a hemispherical surface inclusion (diameter Φ100 μm, depth 50 μm) on the surface of the raceway surface of the bearing. That is, in the embodiment, the maximum diameter of the inclusion corresponds to the diameter of the hole. The life test was conducted under the following conditions. In the life test, contamination was excluded as much as possible, and in the test piece where peeling occurred, when peeling occurred from the indentation, this was excluded from the results.
(Rolling fatigue life test conditions)
Test load: 650kgf
Rotational speed: 1000min ^-1
Discontinuation: 1000h

  The result of the life test is shown in FIG. As shown in FIG. 5, it can be confirmed that Example 1 and Example 2 have a longer lifetime than Comparative Example 1, and it can be seen that compressive residual stress is effective in suppressing the progress of cracks caused by artificial defects. . That is, it was confirmed that by applying compressive residual stress to the raceway surface layer of the rolling bearing, the progress of cracks starting from inclusions existing in the surface layer was suppressed, and the peeling life was extended.

DESCRIPTION OF SYMBOLS 1 Radial ball bearing 2 Outer ring 21 Outer ring raceway 3 Inner ring 31 Inner ring raceway 4 Cage 5 Ball 6 Roller burnishing device 61 Ball

Claims (5)

A rolling bearing that is configured to hold a rolling element freely between an inner ring and an outer ring, and does not share lubricating oil with other parts,
A rolling bearing, wherein compressive residual stress is applied to the surface layer of the raceway surfaces of the inner ring and the outer ring.   In the distribution of the compressive residual stress in the depth direction from the surface of the raceway surface, a peak where the compressive residual stress is maximum is located at a depth of 40 μm or more and 60 μm or less from the surface of the raceway surface. The rolling bearing according to claim 1. A rolling bearing manufacturing method in which a rolling element is rotatably held between an inner ring and an outer ring, and does not share lubricating oil with other parts,
A method of manufacturing a rolling bearing, comprising applying a compressive residual stress to the raceways of the inner ring and the outer ring after the inner ring and the outer ring are quenched and tempered.   When the compressive residual stress is applied to the raceway surface, a peak at which the compressive residual stress is maximized is located at a depth of 40% to 60% of the maximum diameter of the inclusion from the surface of the raceway surface. The method of manufacturing a rolling bearing according to claim 3, wherein the compressive residual stress is applied.   The method for manufacturing a rolling bearing according to claim 4, wherein the maximum diameter of the inclusion is a value in a range of 100 μm or less.

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